That cost me a lot of nerves, but now I can see the light at the end of the tunnel again.
Unfortunately I couldn't solve the problem in #codeberg, I created an issue and am now back in #gitlab.
And here is my clone of the #gluon samples HelloFXML project with gitlab-ci pipeline.
https://gitlab.com/naturzukunft_de/javafx/hellofxml
The generated artifact of the pipeline can be found here.
https://gitlab.com/naturzukunft_de/javafx/hellofxml/-/jobs/10749556038/artifacts/browse
The apk is now also running on my FP 5 with e/OS.
Thanks to @pat_dev for his support